One speculative timeline I saw puts the House Democrats passing impeachment next October, too late before the election for the Senate to hold the trial.
I disagree mildly with your conclusions. I don't think the Democrat leadership, certainly not Pelosi, want to vote on impeachment at all. It's popular with over half the population now but that can change. I think what they want to do is drag it out, as you said, but also count on Trump and team to ignore subpoenas, refuse to appear at hearings, block documents, etc. That way they can have their cake and eat it to. They can go through the motions and have the media cover every obstacle that gets placed in front of them so they can say that they really would like to impeach Trump and are trying to finish gathering the evidence they need to put it to the House, but they are obstructed and blocked at every turn by what they'll describe as the lawless and criminal Trump administration.
A trial is not the Dems goal, rather keeping the false “impeachment” narrative alive and fed daily via media to the voters....
As Levin said...””This entire thing is the Democrat Party in the House seizing control of the instrumentalities of the House bastardizing the impeachment clause in order to drive a trial into the general election.”